[PATCH] teach /proc/kmsg about O_NONBLOCK

If there's nothing available and the file is O_NONBLOCK, return -EAGAIN.

This is a bit grubby - really we should push the file* down into do_syslog()
and handle it inside the spinlock.

fs/proc/kmsg.c

@@ -33,6 +33,8 @@ static int kmsg_release(struct inode * inode, struct file * file)
 static ssize_t kmsg_read(struct file *file, char __user *buf,
 			 size_t count, loff_t *ppos)
 {
+	if ((file->f_flags & O_NONBLOCK) && !do_syslog(9, 0, 0))
+		return -EAGAIN;
 	return do_syslog(2, buf, count);
 }